How to Fill Window Openings With Concrete Blocks

During the course of a big remodeling project, an old window might not be in the best place anymore. If your home is made of masonry materials and you want that window turned into solid wall, concrete blocks are the best answer to fill that opening. This is a fairly straightforward project that can be completed by a do-it-yourself homeowner with intermediate-level skills.

1

Pry the interior and exterior trim off of the walls around the window with a pry bar. Using a reciprocating saw, cut through the screws or nails that attach the side jambs of the window to the blocks in the wall.

2

Move the window sashes to the center of the window, and use the pry bar to fold the side jambs over the top and bottom edges of the window. Take the window out of the wall.

3

Cut through the screws or nails that hold the header (the part that runs across the top of the window) and the sill (the part that runs across the bottom) with the reciprocating saw, and remove the sill and header from the opening.

4

Install wall ties to the edges of the opening by driving a wall plug and screw through the wall ties and into the sides of the concrete blocks on the side edges of the window opening. Use a hammer drill and wear safety goggles when doing this. Place the first two wall ties along the bottom edge of the opening, one on each side of the opening, and two more at every 8 inches along the height of the opening. Wall ties are galvanized metal brackets formed in the shape of the letter L. The short edge of the wall tie is attached to the side of the window opening. The wall ties help lock the new blocks into the wall.

5

Mix a batch of mortar, following the instructions on the packaging.

6

Apply a 1/2-inch layer of mortar with a trowel to the bottom edge of the window opening and along the side edge of the window opening where the first block will be installed. Make sure you place the mortar on the concrete block, and not the drywall on the interior of the building, as the blocks used to fill the opening are being attached to the concrete blocks in the wall.

7

Place the first block into the mortar. Scrape the excess mortar that seeps out from the joints between the wall and the block away with the trowel.

8

Apply mortar to the side of the block you just placed inside the opening and the bottom edge of the window opening. Set the second block into the opening. Lay a level atop the two blocks to check that they are square.

9

Continue laying blocks along the bottom of the window opening until you reach the other side, checking for level as you go.

10

Cut a block in half with the hammer and chisel. Measure and mark the midpoint of the block. Place the tip of the chisel on the line that marks the midpoint, and carefully tap on the chisel with the hammer. Use enough force to create a score line in the side of the block, and keep chiseling until the block cracks. Repeat on the other side of the block. Don't use to much force when doing this, as you can damage the block.

11

Apply mortar to the concrete block in the inside edge of the window opening and the top of the first block you placed inside the opening. Place one half of the cut block into the mortar.

12

Place a full-sized block into the mortar. Lay the level across both blocks. Adjust the full-sized block and half-block until they are level. Continue laying blocks until you reach the other side of the opening, checking for level as you lay them.

13

Continue laying courses of blocks, staggering the joints of each row. When you get to the last course of blocks, apply mortar to the tops of the blocks before you place them inside the opening. If you need to cut the blocks for the last row length-wise to fit inside the opening, use the same process you used to cut the blocks in half, but make the score lines run the length of the blocks, instead of the height.

Things You Will Need

Pry bar

Reciprocating saw

Wall ties

Wall plugs and screws

Hammer drill

Safety goggles

Mortar

Trowel

Hammer

Chisel

Tip

Starting every other row with a half-block keeps the joints staggered, which strengthens the wall.

If a full block doesn't fit at the end of any row, cut a block to the size needed with a hammer and chisel.

About the Author

Carson Barrett began writing professionally in 2009. He has been published on various websites. Barrett is currently attending Bucks County Community College, pursuing a Bachelor of Arts in sports management.